The invention relates to modular, cryogenic, solid rocket propellants with fuel elements of different fuel components, such as fuels, oxidizers, energy-increasing admixtures, binders, additives, etc., for all conventional and other applications of solid rockets.
The invention relates to the technical field of rocket engines and to the manufacture, construction, ignition and combustion construction and the safe storage of cryogenic, modular, solid propellants. In this field, solid propellants are understood to be simple or assembled fuel blocks, which are present in a particular geometric shape, which determines the development of the combustion rate and, accordingly, the propulsion unit as a function of time. The propellant systems can include fittings and extensions, which are mounted according to the state of the art for mechanical reasons as seals, combustion inhibitors or for other reasons and are generally consumed during the combustion.
State of the art solid rocket fuels are propellants of double-base fuels or composite fuel or of combinations of both. To increase the energy, metals such as aluminum may be added. Other additives are added in order to influence the burning behavior, chemical stability or mechanical properties. The components are mixed, shaped and cured into molded objects, which are solid at room temperature, by ingenious methods. Such fuels are referred to as "monergols" (single component systems). According to the state of the art, solid monergol fuel blocks can be stored at a defined temperature range, which includes ambient temperature, such as -30.degree. to +80.degree. C., without melting or changing otherwise within a short period of time. The propellant may contain regions of different compositions and therefore different burning rates (for example, in the so-called dual propellant grains). All aforementioned propellants are referred to in the following as "conventional propellants", irrespective of the fact that these may also contain very exotic components. Conventional solid propulsions have pulses of low to moderate energy ("IsP", a measure of the quality of the fuel as a rocket fuel, the units being in seconds), generally far below 300 seconds. They are produced in very different geometric shapes, but can be divided roughly into two categories, namely into internal burners, which burn off in a more radial direction, and end burners, which burn off in a more axial direction.
Aside from monergolic fuels, fuels are also known, which contain the combustible material and the oxidizer as separate elements in different geometric arrangements. Such arrangements are referred to here as "modular propellants". Modular propellants have the advantage that the burning in diffusion flames takes place as so-called boundary burning, for which the transition to uncontrolled explosions or detonations cannot take place or cannot easily take place. Modular propellants with storable components previously were used only in the form of "sandwich propellants" (with an arrangement of the elements, as in the case of internal burners) and only for burning trials, since the burning properties of monoergolic mixtures are superior to those of modular propellants (see, for example, HANDLEY, J. C., et al., "Combustion of ammonium perchloratepolymer sandwiches", AIAA Journal, 1981, Vol. 19, pp. 380-386). In the area of conventional solid fuels, modularity is of no advantage.
Of the modular fuels, those with encapsulated components form a separate group. The objective of the encapsulation is to mutually separate reactive components and to improve long-term storability. Liquids or very sensitive reactants can be enclosed in capsules. Small capsules are enclosed non-directionally in binders. Macrocapsules can be disposed, aligned and cast with a binder or a curing solid fuel. As the size of the capsule increases, the transition to certain modular fuels is progressive (McCurdy, R. M. et al., "Solid Propellant Grain Containing Metal Macrocapsules of Fuel and Oxidizer", U.S. Pat. No. 3,527,168). As the capsules increase in size to that of rods, as, for example, in the case of modular "rod-in-matrix" propellants, the method of combusting liquids is no longer suitable and, in the case of solid fillers, any type of covering can interfere with the combustion.
A different principle has been proposed, for which the heat of a burning monergol through heat-resistant walls is used for the pyrolysis of fuels and oxidizers, which are then combusted in their own combustion chamber. The geometric arrangement of such pyrolysis elements can be very similar to the geometry of modular fuels (see DE 976 057). On the other hand, the principle of functioning is completely different and the elements, when fitted together, form a rocket with a combustion chamber and nozzle and not a propellant.
Aside from storable solid fuels, frozen fuels were proposed, the components of which are liquids or gases at ambient temperatures. Such fuels are referred to here as cryogenic solid propellants, which is abbreviated as CSP. Monergolic CSP consists of frozen monergols, which are liquid at room temperatures. Modular monergols are composed of frozen elements which, by themselves, are not combustible.
According to the state of the art for modular, cryogenic solid fuel rocket propellants, the fuel elements are isolated chemically from one another by suitably covering the interfaces (U.S. Pat. No. 3,137,127). In particular, the fuel elements can have the shape of disks, the outer surface of which is adapted to the contour of the rocket combustion chamber, while internally one or more boreholes with appropriately shaped cross-sectional surfaces can be present which, by being Linked together, form one or more combustion channels with a constant or variable cross-sectional surface.
The burning of modular fuel elements, which are not monergolic, basically is a diffusive boundary layer burning and, as such, depends on the inflow of reactants. When this inflow is not vigorous, but the result of convection, the reaction is irregular and sluggish, if it takes place at all. This is always the case in internal burners for the uppermost element (furthest away from the nozzle) and, in end burners, from a certain minimum cross-sectional area of the elements onward. Accordingly, convection does not represent a suitable basis for burning in closed combustion chambers, so that the cryogenic modular propellants of U.S. Pat. No. 3,137,127 are not suitable for use.
Recently, cryogenic solids have also become interesting as a base for so-called super high energy chemical fuels (SHET), which consist of energy increasing additives. In the United States (see Carrick, Patrick G., "Theoretical performance of high energy density cryogenic solid rocket propellants", U.S.A.F., Phillips Lab., Edwards A.F.B., Calif., 1995, AIAA-Paper-95-2892), theoretical and experimental investigations have been conducted since 1994 on cryogenic hybrids (that is, diergolic rocket propulsions with a solid and a liquid component). These include also those with frozen fuels, such as hydrogen or kerosene. For hydrogen, the inclusion of atomically dispersed materials is proposed, the high heat of formation of which causes them to be super high energy chemical fuels. The matrix isolation in the hydrogen ice prevents their premature recombination.
Until now, only conventional, storable monergolic solids have been used in practical applications. Modular and encapsulated fuels are not realized either with storable components or with cryogenic components. Aside from the fact that many of the promising fuel components proved to be too poisonous or too corrosive, this is due primarily to the fact that, compared to conventional, monergolic propellants, most of the unconventional propellants described above have a very unsatisfactory burning behavior.
The invention is therefore based on the following problems, all of which show the advantage of using cryogenic, modular solid propulsions. Conventional, monergolic propellants require the processing of large amounts of materials, which basically are explosive. The processing therefore is dangerous and expensive. Modular propellants would therefore be very desirable, because their processing is much simpler. To improve their long-term shelf life, conventional monergolic propellants require certain additives. Nevertheless, however, they are subject to irreversible chemical aging processes. Modular CSP propellants do not need such additives and would be more advantageous because of their much simpler chemical composition. Conventional propellants, insofar as they contain ammonium perchlorate and/or aluminum, greatly contaminate the environment with their exhaust gases. CSP propellants can be prepared on the basis of environmentally friendly liquid fuel combinations. The energy content (IsP) of conventional propellants can be increased only by expensive and dangerous fuel components. Even then, however, the power attained falls far below that of liquid propulsion of moderate to high energy. CSP propellants could make the fuels for liquid propulsion available for solids engines.
The classical fuel combinations with the highest, known, specific pulses require the combustion of metal and so-called chemical hydrogen heating. These triergols cannot be realized in liquid propulsions. Tribrid propulsions (i.e., hybrids with metallized fuel grains, which are combusted by injecting in an oxidizing agent, while additionally hydrogen is being injected in) are complex and difficult to control. The same is true for conventional solid fuels, which are filled with metal and work with hydrogen injection (so-called quasi hybrids). On the other hand, CSP propellants would be exceptionally suitable for metal additives.
Because of the chaotic development of the burning surface, hybrid propulsions tend to deviate greatly from the desired mixing ratio and run very roughly. Modular CSP propellants would be much more suitable for realizing the SHET power units.